Vacuum pump



Oct. 23 1923, 1,471,661

W. G. HOUSKEEPER VACUUM PUMP Filed Aug. 30. 1920 Patented Get. as, ices.

siren STATES inner.

career sates.

WILLIAM GIBBONS HOUSKEEPER, OF NEW YORK, N. Y., ASSIGNQE T WESTERN ELEC- TRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

vAc'uum PUMP.

Application filed August 30, 1920 Serial No. 406,923.

Toallwh-om it may concern:

Be it known that 1, WILLIAM GIBBQNS HOUSKEEP'ER, a citizen of the United States, residing at New York, in the county of New York and State of New York, have invented certain new and useful Improvements in Vacuum Pumps, of which the following is a full, clear, concise, and exact description.

This invention relates to vacuum pumps 1 of the entraining or aspirator type and to methods of operating the same.

In the production of the high vacua employed in vacuum tubes of the pure electron discharge type, it has heretofore been cus tomary to connect a tube to be evacuated to a low vacuum pump, for example a mechanical pump capable of pumping out to a pressure of 10- mm. of mercury or thereabouts and to produce a higher vacuum by the use of an aspirator employing mercury vapor,

connected between the low vacuum or roughing pump and the device being exhausted. An example ofapparatus of this kind is disclosed in the patent to O. E. Buckley, No. 1, i33,258, Oct. 24:, 1922, filed May 8, 1916. Since mercury at room temperatures has a vapor pressure in excess of the pressures desired in vacuum tubes, it has been necessary to provide a trap cooled by liquid air, to prevent mercury vapor from flowing back into the tube being exhausted. This is a dis advantage on account of the expense of and diiiiculty of handling liquid air.

It is an object of this invention to provide a pump employing a pumping medium which at room temperatures, has a vapor pressure less than the pressure desired in the containers being evacuated.

lit is a further object of the invention to employ as a pumpingmedium a substance which may be sublimated or vaporized, from the solid state without passing through an- The invention consists further in the structural and operational details hereinafter described and pointed out in the appended claims taken in connection with the accompanying.drawingain which: Fig. 1 1s a diagrammatic view of a pumping system embodying the principal features oi. the invention, and Fig. 2 is a similar View of the form of the invention which is claimed specifically herein.

[Referring to the drawings by reference numerals, the low vacuum or roughing pump 10 is connected by tubing to the bulb or other device 12 which is to'be evacuated. Forming a part of the tubular connections are the pumping passage 15 and the laterally extending passage 17. Passage 15 is in communication with receptacle 20 containing a substance 21 having the characteristics,

above described as being desirable in a pumping medium.

The parts 15, 17 and 20 are preferably made of pyrex giass, or other substance more refractory than lead glass, and are shown connected to the lead glass tubing 24 by sleeves 25 of platinum.

A heater 30 connected to a source of heating current 32 is provided for vaporizing the substance 21 and a heater 34 may be pro-- vided to prevent the vapor from solidifying during its passage through tube 15.

The pumping medium 21 is preferably a substance which has a low vapor pressure at room tern era-tures. llhis avoids the necessity of'a liquid air trap. Preferably a substance is employed which may be vaporized at moderate temperatures and which has a relatively high vapor pressure at a temperature less than its melting temperature. Zinc, arsenic, ammonium chloride and iodine are substances which'will sublime under vacua which may be produced by a roughing pump such as above described. In other words their boiling points under these pressures are lower than their melting points. Zinc, forexample, at a temperature slightly under its melting point, has a vapor pressure of 10- .mm. of mercury, and wili. freely give of? vapor from the solid condition if the roughing pump is operated to reduce the pressure below this amount.

The operation. of the device shown in Fig. 1 using zinc/as a pumping medium is as follows: the pump 10 is operated until the pressure is reduced to the neighborhood of 10 mm. of mercury. The chamber 20 and passage 15 are then heated to the melting point of zinc, 419 C. The pump 10 is continuously operated-and a stream of zinc vapor flows through passage 15, entraining with it the gas from passage 17 and bulb 12, until the pressure in the latter is gradually reduced to the required value. The methods employed for measuring the vacuum in bulb 12 are well-known and need not be described here.

Two methods in general may be employed for the return of the zinc to chamber 20. As shown in Fig. 1, relatively narrow tubing may be used and the zinc vaporized at a suf ficiently rapid rate to increase the pressure in passage 15, so that-the major portion of the vapor will be condensed in liquid form and will flow back to chamber 20. On the other hand the size of the passage and the rate of vaporization may be so proportioned that the pressure at all points is lower than the vapor pressure of zinc at its melting point. Under these conditions the vapor, when cooled to approximately room temperature, will solidify or freeze to walls'of the tubing. The solid zinc may be periodically melted at atmoshperic pressure and allowed to flow back to chamber 20.

A more economical method of employing zinc, or other substances which sublime, can be carried out by the apparatus shown in Fig. 2. This method falls generically under the second method described above. The passage 15, corresponding to passage 15 in Fig. 1, is provided at opposite ends with chambers 40 and 41 surrounded by heaters 43 and 44 respectively. These heaters are alternately supplied with heating current from source 32 by reversing the switch 46. Passage 17 is connected to an intermediate point on passage 15' and passages 50 and 51 lead from points near the extremities of assage 15' to a three way valve 55, so that t e lastmentioned passages may be alternately connected to the roughing pump 10.

In operation one of the chambers 40, 41 is initially supplied with zinc, or the like. Suppose chamber 40 is so filled. Then valve 55 is turned so that the evacuation takes lace through the opposite passage 51.

hamber 40 is heated and a stream of zinc vapor flows through passage 15 with the aspirating ellect above described. Chamber 41 is at approximately room temperature and the vapor condenses and collects therein in solid form. When the transfer of zinc from one chambe to the other is as nearly complete as is desirable, switch 46 and valve 55 are reversed and the exhaustion continues through passage 50, the vapor stream flowing in the opposite direction. As is apparent, these reversals cf the operation may be continued indefinitely and the efiicienc from the standpoint of heating current will be at a maximum. Obviously, valve 55 and switch 46 may be mechanically connected for s1- multaneous operation if desired.

It-will benoted that when zinc is employed as a pumping medium, it is unnecessary to cool any portion of the tubing below room temperatures, since zinc will solidify atroom temperatures and has at such temperatures a vapor pressure less than the pressures ordinarily obtained in pumping out a vacuum tube to be employed as a pure electron discharge device.

While this application is specific to the use of a pumping medium having a volatilizing temperature less than its melting temerature, my copending application Serial 0. 478,975 filed June 20, 1921, discloses and claims broadly the use as a pumping medium of a substance having at room temperatures a vapor pressure less than that desired with-in pure electron discharge devices, whereby the use of a liquid air trap is avoided.

What is claimed is:

1. The method of operating a vacuum pump having an opening thereinto from a container to be evacuated which comprises vaporizing a solid substance, causing the resultant vapor to flow adjacent said opening, and condensing said vapor in solid form.

2. The method of operating a vacuum pump having an opening thereinto from a container to be evacuated which comprises heating to a temperature less than its melting temperature asubstance having relatively high vapor pressure at a temperature below its melting temperature, causing the re sultant vapor to flow adjacent said opening, and condensing said vapor in solid form.

3. The method of operating a vacuum pump having an opening thereintofrom a container to be evacuated which comprises vaporizing a solid substance and causing the resultant vapor to flow adjacent said opening.

4. The method of o crating a vacuum pump having an openlng thereinto from a container to be evacuated which comprises vaporizing a solid substance and causing the resultant vapor to flow transverse to said opening.

5. The method of operating a vacuum pump having an opening thercinto from a container to be evacuated which comprises sublimating a solid substance and causing the resultant vapor to flow adjacent said opening.

6. The method of pumping which comprises vaporizing a substance, causing the resultant vapor to flow in one direction, condensing the vapor, accumulating the condensed substance then revaporizing the condensed substance, and causing the vapor to flow in another direction.

7. The method of pumping which comprises vaporizinga substance, causing the resultant vapor to flow in one direction, condensing the vapor, accumulating the condensed substance, then revaporizing the condensed substance, and causing the vapor to flow to tion.

8. A vacuum pump comprising a pumping chamber, a supply of-pumping medium which may be converted from the solid to the gaseous state without passing'through the liquid state, and means for vaporizing said pumping medium to establish a vapor stream traversing said pumping chamber.

9. A vacuum pump comprising a pumping chamber, a supply of pumping medium which at aitemperatu're below its melting point has vapor pressure greater than 10-- mm. of mercury, and means for vaporizing said substance to establish a'vaporstream fiowin through said pumping chamber.

10. vacuum pump comprising a pumping chamber, a supply of pumping-substance which has a relatively high vapor pressure at temperatures belowits melting point, and means for vaporizing said substance to establish a vapor stream through said pumping chamber.

11. In a vacuum pump a pumping chamber, a body of zinc therein, and means for and condense in; its original loca-,

sage, connections from opposite en vaporizing said zinc to establish a vapor stream flowing through said pumping chamber.

12. In a vacuum pump, a pumping passage, means for vaporizing a solid substance and causing it to flow through said passage, means for condensing said substance in solid form at the termination of said passage, and means for revaporizing said substance 1 and causing it to flow through said passage in the reverse direction.

13. In a vacuum pump, a pumpi pasf- 0 said passage to a three way-valve for alternate connection to a low vacuum pump, and a connection intermediate said ends to a container to be evacuated.

14. In a vacuum pump, a pumping pas sage having a connection to a container to be evacuated, the ends of said passage being adapted to be alternately connected to a lowvacuum pump, receptacles for a pumping medium in communication with the respective ends of said passage, and means for alternately heating said receptacles.

In witness whereof, I hereunto-subscribe my name this 23r d day of August, A. D.,

WILLIAM GIBBONS HOUSKEEPER. 

